ARCHAEA

Archaea were only shown to be a separate domain—through analysis of their RNA—in
1977. Many archaea thrive under the extreme conditions of hot sulfur pools or in
minerals and rock deep inside the Earth. On the floor of the ocean at thermal vents,
lacking both sunlight and oxygen, they obtain energy and nutrients from chemical
reactions with energetic molecules emerging from the vents and molecules on the
mineral surfaces of rocks.

Branch: Methanobacteriales

Example: M.
smithii

Three main groups of hydrogen-consuming microbes make their homes in the human
gut where they aid in digestion—turning nutrients into calories. They include
acetogens (anaerobic bacteria that generate acetate), sulfate-reducing bacteria,
and methogens such as M. Smithii, the most abundant methanogenic archaeon
in the human gut and an important player in the digestion of polysaccharides
(complex sugars). The build up of hydrogen in the gut reduces the efficiency of
the digestive process; M. Smithii and other methangenic archaea help to
remove excess hydrogen. Studying these microbes is helping researchers
understand how hydrogen metabolism affects the digestion of various dietary
components. Targeting M. Smithii could lead to new treatments for obesity
and anorexia.

*Note: not all branches are shown in the tree diagram

Branch: Methanococcales

Example: M.
jannaschii

Image copyright Dennis Kunkel Microscopy, Inc.

Methanococcus jannaschii (also known as Methanocaldococcus
jannaschii) was discovered living in the extremely hot and oxygen-deprived
waters at the base of a white smoker chimney in the deep ocean, and was the
first archaeon to have its genome fully sequenced. The majority of its genes
related to energy production, cell division, and metabolism were found to be
most similar to those found in bacteria, while those related to transcription,
translation, and replication were found to be most similar to those found in
eukaryota. Methanococcus is a genus of methanogens, or methane producers.
Methanogens are extremely important in environments that are anaerobic (lacking
oxygen) because as they convert organic compounds into methane they provide
pathways for compounds that exist in anaerobic environments to escape into the
atmosphere. Methanococcus jannaschii produces many unique cofactors,
coenzymes, and enzymes during methanogenesis—macromolecules that could be
valuable in biotechnology applications.

*Note: not all branches are shown in the tree diagram

Branch: Halobacteriales

Example: unknown

Image copyright Dennis Kunkel Microscopy, Inc.

This extremophile of unknown genus (likely, Halomicrobium sp. or Halobacterium
sp.) was found growing at high salinity (2.5 times the concentrations in
normal sea water). It is an example of dramatic variations in the size or shape
of the cell called pleomorphism. Halobacteriales are an order of the
Halobacteria found in water saturated or nearly saturated with salt and are
common wherever large amounts of salt, moisture, and organic material are found.
Halobacteria require oxygen and are incapable of fixing carbon from carbon
dioxide but can survive in salty environments because of their unique way of
creating energy through photosynthesis that is different from other forms of
photosynthesis that use chlorophyll. Large halobacteria blooms appear reddish,
from the pigment bacteriorhodopsin. This pigment is used to absorb light, which
provides energy to create ATP. A second pigment, halorhodopsin, is used to pump
in chloride ions in response to photons, thereby creating a voltage gradient and
assisting in the production of energy from light.

*Note: not all branches are shown in the tree diagram

Branch: Branch Unknown

Example: "microcholla"

P. Boston

Who are they? Are they Archaeal ancestors? No one knows. In a Scanning Electron
Micrograph (SEM) image, these mysterious reticulated filaments look like fishnet
stockings. They have been nicknamed "microcholla" because their appearance also
recalls the dried remains of dead cholla cactus branches that are found
scattered across the landscape of the American Southwest. Fuzzy-looking
actinobacteria are in the background. These organisms from Maelstrom Lavatube in
Hawaii are found growing in a blue-green copper mineral (hydrated copper
silicate) called chrysocolla.

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